Wild Bird Migration Blamed for Avian Flu Outbreak

Global transportation of pathogens not limited to humans

The highly pathogenic avian influenza (HPAI) H5N8 virus outbreak which swept across 21 U.S. states from late 2014 to mid-2015 was likely spread by wild birds migrating from South Korea to Japan, North America, and Europe, according to findings from an international consortium of researchers.

The virus, which resulted in the destruction of close to 50 million chickens and other commercially-raised birds in the U.S., was the worst bird flu outbreak in American history. The economic loss in the U.S. alone was estimated to exceed $3 billion in direct and indirect costs.

No human transmissions were reported in the U.S., but earlier outbreaks have resulted in infection, serious illness, and death in parts of Asia where people live in close contact with domesticated poultry.

The 2014-2015 outbreak began in South Korea, where HPAI strain H5N8 affected poultry in the winter of 2013 and 2014. It spread to Japan, North American and Europe, causing outbreaks between autumn of 2014 and early summer of 2015, members of the Global Consortium for H5N8 Related Avian Virus wrote in the journal Science, published Oct. 13.

Consortium member Samantha Lycett, PhD, of the University of Edinburgh Roslin Institute in Scotland, told MedPage Today that while chickens sickened by the H5N8 virus usually die within days, this does not seem to be the case for ducks and geese.

"Because these migratory birds are not as sick they can still fly," she said. "So we have the potential for a long-range spread via wild, migrating birds."

Monitoring the migration routes of wild birds may provide valuable information about future bird flu outbreaks before they occur, the researchers concluded.

The group noted that it has not been clear exactly how HPAI H5N8 virus spread so rapidly around the world. The newly published analysis represents a pooling of resources and data from 32 separate institutions across the globe, with the aim of analyzing the available genetic, epidemiologic and ornithological data related to the outbreak.

"For this purpose, we performed phylogeographic analysis of HPAI H5N8 viruses detected in wild birds and poultry from this global outbreak," the researchers wrote. "In addition, we analyzed migration patterns of wild birds found infected with HPAI H5N8 virus, epidemiological investigations of HPAI H5N8 virus outbreaks, and poultry trade records from countries where HPAI H5N8 virus was reported."

The analysis revealed that the main routes of large-scale geographical spread of HPAI H5N8 were most likely via long-distance flights of infected wild birds, beginning in South Korea or other unsampled locations in the spring of 2014 to northern breeding grounds. By autumn of 2014 the virus spread from these breeding grounds to migration wintering sites in North America and Europe.

"Recognition of a likely role of wild birds in the spread of HPAI reinforces the need to improve biosecurity on poultry farms and to exclude wild birds from the immediate vicinity of poultry farms," the researchers wrote.

Lycett said biosecurity efforts designed to keep commercial fowl and migratory foul separate could help prevent or slow the spread of future avian flu outbreaks. She declined to speculate on whether the recent proliferation of free-range, commercial chicken farms contributed to the 2014-2015 outbreak.

"Culling wild birds, draining or disinfecting wetlands would not be effective," the researchers pointed out, "because these viruses disseminate on rapid time scales over very large distances, making reactive interventions of this kind impractical." However, they did not specify biosecurity measures better suited to protect commercial flocks.

This study was funded by the European Union's Horizon 2020 research and innovation program COMPARE.

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